Cathode ray tube noise gate system



March 17, 1936.l J. F. DREYER, JR; am. 2,034,565

cuaon im TUBE NoIsE GATE SYSTEM Filed sepf. 25, 1934 ATTORNEY Patented' Mar. 17, 1936 PATENT OFFICE 2,034,565 cArnonE RAY TUBE NoIsE GATE SYSTEM John F. Dreyer, Jr., Brooklyn, N. Y., and Richard Tempel Orth, Maplewood, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application September 25, 1934, Serial No. 745,394

6 Claims.

O ur present invention relates tovamplication control systems, and more particularly to a novel and improved system for automatically regulating the gain of the audio and radio amplifiers of a signal receiving system and simultaneously indicating the resonance. condition of the system.

Signal receiving systems are customarily equipped at the present time with automatic volume control circuits. It is, also, usual to provide such receiving systems with resonance in dicators so that the tuning of the system is rendered vcomparatively simple. Furthermore, and in order to avoid or minimize interchannel background noises, radio receivers equipped with automatic volume control circuits have been `provided with muting, or squelching, networks. From the viewpoint of economyin set production, it is obvious that the resonance indicator, as well as the muting network, should' involve asv few circuit. elements 'as possible. Additionally, the muter circuit, regardless of its point of application in the transmission system, should be highly eiiicient and positive in muting action.

Accordingly, it may be stated that it is onev of the main objects of our present invention to provide a, unitary electrical instrumentality in a radio receiver equipped with automatic volume control, which instrumentality is of the cathode ray type, and not only functions to visually indicate the resonance condition of the receiver While -the receiver is being tuned, but simultaneously functions as a noise gate, or muting device, in order to suppress background noises which are usually amplified when the received signal y intensity falls below a-predetermined minimum value.

Another important object of the present iny functions-resulting in 'a visual indication of the resonance status of. the receiver, while the other function results in an impairment of the transmission efliciency of the receiver when the received signal intensity decreases below a predetermined magnitude.

" provide a novel type of-cathode ray tube for' a Another obje'ct of our present invention is to radio receiver, the tube being capable of funcf tioning as a combined noise gate and tuning indicator, and the tuning indication being provided on an electrode of the cathode ray tube which is provided with a coating of electronresponsive material.

(ci. o-2o) Still other objects of the present invention are to improve generally the simplicity and em` taken in connection with the drawing in which we have indicated diagrammatically a circuit organization whereby our invention may be car ried into effect. i

In the drawing:

Fig. 1 shows a radio receiving system embod ing the present invention,

Fig. 2 shows a cathode ray tube embodying the present invention when viewed from the indicator side of the tube.

Referring now to the accompanying drawing, 'there is shown in Fig. 1 a radio receiving system of a conventional type. Since the combined noise gate and tuning indicator of the present invention is independent of the type of radio receiver utilized, as well as independent of the nature of the automatic volume control network, the various circuits of the receiving system up to the audio frequency amplifier have been conventionally designated. For example, the reference characteristic A denotes the usualsignal collector, such as a grounded antenna circuit. The signal collector is coupled to a radio frequency ampliner l, and the output of the radio frequency amplier is impressedupon a detector 2.v The detected output of the detector 2 is impressed upon an audio frequency amplifier 3 through a coupling transformer 4, and the audio output of tube 3 may be further utilized in additional audio amplifiers, or in a reproducer.

These elements are, in general, the usual networks embodied in a radio receiving system. vThe reference numeral 5' denotes the customary sy m.

fier networks feeding the audio demodulator, or second detector.

In any case, the numeral 2 denotes the audio demodulator of the receiving system, and the numeral 5 designates the tuning means of the receiver, which tuning means may be adjusted throughout the tuning range of the receiver; the tuning range may be, for example, in the broadcast range.

The automatic volume control mechanism of the receiver, being independent of the combined noise gate and tuning indicator, has been conventionally represented. The automatic volume control may be provided by feeding a portion of the signal input to the audio demodulator 2 to a rectifier which functions to convert the signal currents to a rectified current, and the rectified current will then be used to vary the grid bias of the radio amplier tubes. Since such systems are very well known to those skilled in the art at the present time, it is believed merely necessary to denote the network in conventional form and make general reference to such systems known in the prior art so that those skilled in the art may readily construct the present invention. An automatic volume control system which may be used in connection with lthe present invention is disclosed by Chittick and Carlson in application Serial No. 642,544, filed November 14th, 1932,

A radio receiver of present day construction is highly sensitive and selective, and side band cutting will result unless the receiver is tuned to precise resonance with the desired carrier frequency. In the case of a radio receiver equipped with automatic Yvolume control, this disadvantage is marked, and becomes even more aggravated by the fact that ear tuning is practically impossible. For this reason visual tuning indicators have been proposed for use in connection with radio receivers provided with automatic volume control.V

Again, whenever the tA ""g means 5 of a receiver provided withautomaticvolume control is adjusted to a point such that no signals are received, the automatic volume control network `is not operating, and this increases the amplifunctions of muting and tuning indication areperformed by a single instrumentality.

'I'his instrumentality comprises a. cathode ray` tube, generally denoted by the reference numeral 5, and it will be recognized that the cathode ray tube has been conventionally represented. The cathode ray tube 5 is substantially similar in con-- struction to tubes of this type well known to those skilled in the art, and differs from such well known tubes in the details to be hereinafter described. The tube 5 generally has the shape shown and is provided with the usual cathode 6, the cathode being of the indirectly heated type. focussing cy.- inder 'I and electrodes 8 and 9. 'I'he electrode 9- is disposed in the same plane as the electrode 8, but the electrode 8 is of a substantially greater length than the electrode 9. Both electrodes have the same width, and, as shown in Fig. 2, they are both made of a mesh material and coated with willemite.

The willemite material is well known to those skilled in the ar, and is commonly employed for coating the inner face of the viewing face 9 of the cathode ray tube 5. For reasons to be given at a later point the willemite is not applied toA The electron beam emitted from cathode 6, and

focussed by cylinder l, is displaced along the length of electrodes 8 and 9 by the varying magnetic leld provided by coils I0 and I I. These two coils, providing magnetic deflection of the electron beam, or stream of cathode rays, are simply connected in series in the plate supply of the controlled radio frequency amplifier tubes. 'Ihey are conventionally represented, but are to be understood as having their axes in alignment, and their common axis at right angles to the axis through electrodes 8 and 9.

Accordingly, the lead I2 has been shown connected to the plates of the radio frequency tubes,

' and the plate supply lead I3 is shown connected to the positive terminal of the energizing direct current source generally denoted by the reference letter P. It will be understood, of course, that the resistor, or potentiometer, P is the usual bleeder resistor connected across the power supply network, which network may include the usual alternating current rectifier and filter system. An intermediate point of the bleeder P may be grounded, as at I4, and the focussing cylinder may be connected to a point I5 on bleeder P which is intermediate the negative -side of the bleeder and the ground point. 'Ihe electrode 8 is grounded, while the electrode 9 is connected by lead I6 to the signal grid of audio amplifier 3 through a path which includesra filter resistor I'I, the manual volume control resistor I8, and the adjustable tap I9.

The resistor I8 is connected across the secondary of coupling transformer 4, and the cathode of the audio amplifier 3includes the usual grid bias resistor 20, by-passed bycondenser 2|, the grid bias resistor being connected to ground so as to provide a return path to the energizing network.

It will also be noted that the lead I6 is connected to a. point intermediate resistor I'I and a secondary resistor 22 which functions as the cathode ray tube auxiliary plate resistor. One side of resistor 422 is grounded, and a by-pass condenser 23 is connected between the low alternating potential side of resistor I8 and ground.

In Fig. 2 is shown the appearance of the viewing end of the cathode ray tube 5 both in the case when a station has been tuned in, and when there is no station being received. The dotted lined rectangle 38 designates the appearance of the image of the rectangular slit 3I of focussing cylinder 1, which image appears upon the electrode 8 when a station has been tuned in. The image 38 is,of course, caused by the electron beam which passes through the slit 3| and impinges upon the inner face of electrode 8. The electronsfstriking the Willemite coating of the electrode 8, cause a fluorescence, or glow, and thus a glowing rectangular area appears on the electrode 8.v 'I'he dark rectangular area 32 appearing on electrode 9, in Fig. 2, shows the position of the area 32 when no station is being received. It will be observed that the electron beam has been deflected from electrode 8 to electrode 9. In other words as the resonance condition of the receiver varies, the rectangular image of electrodes 8 and 9 varies in its position, andthis is due to the magnetic deflection caused by coils I8 and I I.

Since the flow of current through thepath in-A cluding coils I and Il isa minimum when the tuning means 5 has been adjusted to exact resonance with a desired carrier, it necessarily follows that the magnetic deflection of the electron beam will be a minimum, and, therefore, at exact resonance the rectangle 38 will be adjacent the top of electrode 8. As the set is tuned away from resonance the plate current flow through coils I8 and Il will increase, and the electron beam will slowly move down the electrode 8 until it appears on the Aelectrode 9. In this way, the user of the set can readily tell not only whether or not the set is in tune to a :desired station, but can also tell whether or not the set is in exact resonance with the desired carrier.- Of course by varying the configuration of slit 3l, or disposing a plate between focussing cylinder 'l Aand electrodes 8 and 9, which plate has a beam aperture of any desired design, the image on the electrodes 8 and 9 can be'made to have any desired configuration. For example, the image can take the form of a trade-mark, or any fanciful gure. Such a plate could be placed between the cylinder 1 and coils l0, Il. This plate would, also, be connected to bleeder P at a point between points I4 and I5. i.

The beam current in the cathode ray'indicator is considerably high, and can be of the order of 100 micro-amperes. Since this is the case, the

beam current can be utilized to secure the noise gate function. The electrode 9 receives the electron stream when signals are not tuned in, or are not sufficiently strong to deilect the beam upon electrode 8. Since the electrode 9 is connected by a direct current path to the grid circuit of audio amplifier 3, it will be seen that when the beam strikes the electrode 9 adirect current voltage is produced. A

When applied to the grid of audio tube 3, this voltage is of sufficient magnitude to bias the audio tube substantially to cut-off. Thus, the transmission through` tube 3 to the reproducer is rendered highly inemcient, and the receiver has been silenced. It'will, of course, be understood that when 'the electron beam is focussed upon electrode 8, there is provided on the grid of audio amplier 8v the normal operating negative bias produced across biasing resistor 20. As soon as the electron beam strikes electrode 9, however, an additional negative bias is applied upon the grid of the audio tube, and produces the silencing action.

Obviously thedirect `current path between electrode 9 and the signal transmission network may be applied to any other point in the receiving system, the essential requirement being to produce an auxiliary negative biasing action upon an'electrode, which auxiliary biasing action results in ineflicient transmission through the receiving network. An important advantage in coating electrodes 8 and 9 with the willemite material, and not disposing it upon the inner face of viewing disc 9' as is usually done, resides in Ithe fact that no secondary electrode emission is encountered. If the willemite material were disposed upon the inner face of disc 9' as is customarily done, sufcient secondary emission would be encountered whenthe set was in tuned condition to perform silencing of the audio ampliiier. Byl providing the electrodes 8 and 9 with parting from the scope of our invention, as set forth in the appended claims.

What is claimed is:

1. In combination with a radio receiver provided with an automatic volume control network, a combined noise gate and tuning indicator characterized by the fact that the indicator comprises a cathode ray tube lincluding a pair of electrodes provided with fluorescent material, one of said electrodes being connected to a point of fixed potential, and the other electrode being connected to said point through an impedance, means for producing an electron beam within the tube, means for magnetically deflecting the electron beam within the cathode ray tube in accordance w'ith variations in received signal intensity, and a direct current connection between a gain control electrode of a transmission tube of said receiver and the electrode side of said impedance.

2. In a system as de flnedvin claim 1, said magnetic deflection means comprising a pair of coils arranged in the plate current supply lead .of the radio frequency amplifier of the receiver. v 3. In a system as defined-in claim 1, said pair of electrodes being disposed in a common plane, and said fluorescent material being such that a luminous indication appears on the electrodes whenever the electron beam impinges thereupon.

4. In a radio receiver including`a radio frequency amplier, an audio demodulator and an audio frequency amplifier, automatic volume control means for maintaining thesignal input intensity to the audio demodulator substantially constant regardless of signal input variations in the radio frequency amplifiersinput, a cathode ray tube provided with means for producing an electron beam and a pair -oi electrodes, means electrically connected with the plate current supply of the radio frequency amplier for magnetically deecting the electron beam in response V the other electrodebeing connected to said point through an impedance, and a direct current connection between a gain control electrode of said audio ampliier'and thev electrode side of said impedance whereby said audio amplifier is rendered highly ineicient with respect. to electrical transmission when the electron beam falls upon said other electrode.

5,; In a signal reception system of the type provided with a signal transmission tube network, a demodulator network and an audio amplier tube network, means for automatically regulating the transmission efficiency of said transmission network in response to varations--inreceived signal amplitude in a sense to maintain the signal amplitude at the demodulator input substantially constant, a cathode ray tube provided with at least means for producing an electron beam and a pair of electrodes, one of said electrodes being connected to a point of relatively nxea potential, and the other electrode being con- "5 beam falls upon said other electrode.

6. In a signal reception system of the type provided with a signal transmission tube network, a demodulator network and an audio amplier tube network, means for automatically regulating the transmission eiliciency of said transmission network in response to variations in received signal amplitude in a sense to maintain the signal amplitude at the demodulator input substantially constant, a cathode ray tube provided with at least means for producing an electron beam and a pair of electrodes, one of said electrodes being connected to a point of relatively fixed potential, and the other electrode being connected to said point through an impedance, means, responsive to variations in the space current ilow of said signal transmission network, for deflecting the electron beam upon said one electrode when signals of a desired amplitude are received and upon said other electrode when the amplitude of said signals falls below a predetermined intensity level, and means operatively associated with at least one of said networks and the electrode side of said impedance whereby said one network is rendered inefiicient with respect to signal transmission when the electron beam falls upon said other electrode,

. and said pair of electrodes being provided with a coating of fluorescent material whereby a luminous indication appears cn the electrodes whenever the electron beam impinges thereupon.

JOHN F. DREYER, JR. RICHARD T. ORTH. 

